Current methods of synthesizing ethanol-amines involve reactions of ethylene oxide and ammonia. Because of its flammability, toxicity-(permissible worker exposure levels are 1 ppm), and volatility, an alternative feedstock to ethylene oxide would be desirable.
The prior art contains teachings of the use of ethylene glycol (EG) as a feedstock for ammonolysis reactions using both supported and non-supported catalysts. No known references disclose the use of soluble catalyst systems. Those references which teach use of ethylene glycol, however, always operate their processes under ammonia-rich conditions in order to avoid the predominant side reactions and production of undesirable cyclic byproducts which occur under ammonia-lean conditions.
Previous methods involving reactions of ethylene glycol and ammonia are typified by U.S. Pat. No. 3,137,730 to Fitz-William. As taught by Fitz-William, a large excess of ammonia (i.e., at least 5 mols NH.sub.3 per mol glycol) is reacted with ethylene glycol over a heterogeneous copper/nickle catalyst supported on alumina. The product of such a reaction is ethylenediamine rather than ethanolamines. In fact, the results reported by Fitz-William fail to indicate any production of ethanol amines.
U.S. Pat. Nos. 4,123,462 to Best also teaches the reaction of large excesses of ammonia with ethylene glycol. As taught by Best, a heterogeneous nickel-rhenium catalyst is used to produce, among other products, ethylenediamine and piperazine (using EG:NH.sub.3 ratios of from 1:4 to 1:20). Best notes a production of ethanolamine (column 18, line 61-3) but quantifies this production only as a relative GC area ratio to the production of piperazine. Furthermore, only monoethanolamine (MELA) is reported by Best as a reaction product.
British Pat. No. 813,957 describes the production of 2,5-dimethyl piperazine from a 2:1 mixture of ammonia and propylene glycol over a heterogeneous Cu/Cr/Ni catalyst. Such a reaction typifies the production of cyclic products in ammonia-lean reaction systems. Because of this tendency to produce cyclic products under low ammonia conditions, the prior art has taught the use of excess ammonia (see "Ethylenediamine by Low-Pressure Ammonolysis of Monoethanolamine", Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 399-407 by C. M. Barnes and H. F. Race). As taught by Barnes and Race, the prior art suggests two possible paths for reactions of ethylene glycol with ammonia. At high ammonia to ethylene glycol ratio, ethylenediamine appears to be a predominant product, while at lower ratios, piperazine might be expected to predominate.